Defragmenting RAID (logical) disk(s)....

Hi,
For the particular system in question, we have a 1.5TB "disk" (RAID 5) which is currently more than 75% "externally" fragmented.
I am looking at several defragmenting tools such as Diskkeeper, PerfectDisk, etc. but I need to know in advance about how long it would take to defrag a volume this size so I can plan for down time.
Certainly I don't expect an exact number, but I would like a best case to worst case scenario.
I personally have not yet defragmented a RAID disk and am looking to benefit from those of you experienced with this sort of thing.
Thanks!

There are too many factors to predict how long this will take. But Diskeeper has the ability to defrag SQL Server files on the fly. On other words, you don't need to have any down time. Install Diskeeper and set it to run during slow times of the day, and at some point, it will catch up and defrag your physical files. This might take some time, but it will eventually get done. I think there is a white paper on the Diskeeper website talking about how to best defrag RAID arrays.

Hi Brad,
Thank you for taking the time to reply.
I realize there are varying elements to this equation, but as I said I am just looking for ballpark. If I chose not to let the defragmentation tool run on the fly, how long would you guesstimate it would take...a day, several days....a week?
Thanks!!!

We've done a Windows defrag on a 3TB RAID 5 array and it took about 4 days (if I remember correctly) to give you an estimate.
Something to keep in mind is how big your db files are. If there isn't enough free space for a large db file to be moved then Windows defrag will not help you much. Sometimes it is better to backup the databases (or the large ones at least), drop them from your array and then do the defrag. Afterwards you just restore the backups and it should sort out most of your fragmentation of your db files.
Hope this helps.